The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention pertains to leak detection techniques and devices, more particularly to the use of vacuum tests and devices to detect the presence of leaks, and most particularly to using a vacuum test to detect the presence of leaks and identify the seals where leaks have occurred.
2. Description of the Related Art
Modern weapon systems, such as torpedoes and missiles, are a collection of subassemblies that are housed in shell sections. Individual shell sections are connected together with seals. After final assembly, the currently used methods to verify the integrity of the seals are by pulling a vacuum or conducting a pressure test. Seals are flexible and work by forcing the flexible sealing material into/against the two mating parts. Seals are designed for high internal pressure or high external pressure. Therefore, seals have a direction of use associated with their intended use and should be tested in that direction. For systems with high internal pressure a pressure test is used. In conducting a pressure test once the system has been pressurized an initial internal pressure reading is taken. Then the system is allowed to set for a period of time, usually about 30 minutes, and the internal pressure is again measured and, then, compared with the initial level. Pressure changes that exceed a nominal amount are an indication of a bad seal(s) in the system. The leak rate is a fraction of the pressure applied across the seal. Moderately high pressures are used to quickly indicate small leaks.
For systems with high external pressure (under water systems), the direction of the desired seal requires that test pressure should be greater outside the system than inside. It is impractical to construct large high pressure chambers to surround the system under test.
The only method remaining to verify the integrity of a seal for an underwater weapon is to pull a vacuum inside the weapon. Even if a perfect vacuum is used, only 14.7 psi can be applied across the seal. Leaks can be difficult to detect with this low of a pressure differential. A longer observation time helps to some degree in overcoming this shortfall, but is obviously more cumbersome and costly.
Another problem with both of the tests described above is that even if a leak is detected, this merely indicates that one or more of many seal may have leaked. A modern torpedo may have over a dozen seals that are being tested. A common practice after determining a possible leak condition, is to backfill the cavity on the weapon with a gas at a slight positive pressure to check for the presence of the gas around the individual seals. The gas would escape around the defective seal(s). The gas of choice was FREON 12. Recent regulations have attempted to discourage this practice. Other types of Freon gases are currently being used. However, extremely expensive leak detectors must be employed when using this method.
Therefore, it would be desired to provide a leak detection device and technique that could be used for any type of weapon system that could detect leaks and identify the faulty seal(s) associated with said leaks.
The present invention comprises a device and a method for determining if a system with multiple seals has a leak and, if so, which of the multiple seals is causing said leak. The device and method employ a change in the optical reflectivity of a transparent, plastic membrane to make the above mentioned determination.
Accordingly, it is an object of this invention to provide a device and method to detect leaks in systems containing seals.
It is a further object of this invention to provide a device and method to detect leaks in systems containing seals that is simple and cost efficient.
A still further object of this invention to provide a device and method to determine the specific seal(s) that is leaking within a system containing multiple seals.
This invention accomplishes these objectives and other needs related to leak detection by providing an optical leak detection device for seals or joints comprising a transparent plastic membrane which is placed around the outer edges of the seal or joint being tested. Adhesive/sealant is applied around the edges in order to ensure that the membrane adheres around the seal or joint and also to form a gap between membrane and the seal or joint. Because the membrane adheres to the adhesive without contacting the seal or joint, the surface of the membrane is optically reflective and possesses a xe2x80x9cglossyxe2x80x9d look. A means to pull a vacuum is employed on the seal or joint on the side opposite to the membrane. If no leak exists in the seal or joint, the membrane stays in place and the optically reflective surface remains the same. However, if a leak exists, the membrane will be pulled into contact with the seal or joint, removing the gap, and the surface of the membrane becomes optically diffuse. The difference between the optically reflective and optically diffuse surfaces is obvious to the person using the device, and, thereby, one can easily detect a leak. The device and method of the present invention may be applied to seals or joints on a variety of one dimensional and two dimensional curved surfaces in addition to flat surfaces.